This invention relates generally to an aircraft heater floor panel and, more particularly, to an aircraft floor panel including a plurality of layers cured to form a lower support level, an upper heater level, and a top metal sheet for protecting the underlying layers from floor-traffic related damage.
An aircraft will commonly include heated floor panels in order to maintain the cabin at a comfortable temperature. The floor panel is typically supported by an aircraft structure and has a structural integrity sufficient to support the weight of people and objects resting on top thereof. A metal face sheet typically forms the top surface of the panel to protect the underlying layers from punctures from high heels, chips from dropped objects, scratches from dragged luggage and/or other floor-traffic related hazards.
An aircraft heated floor panel is usually made by compiling a series of layers together to form a lower support level and an upper heater level. The lower support level may include, for example, a honeycomb layer surrounded by reinforcing fiber layers. The upper heater level may include, for example, a resistance element disposed in layers of a thermosettable dielectric material. High temperature film adhesives and scrims are appropriately provided between the layers and the compiled layers are cured at an elevated temperature (often in excess of about 250xc2x0 F.) to form a composite structure.
The composite structure is then cooled to room temperature and the metal face sheet is secured to the previously cured layers in a separate manufacturing step. Specifically, for example, an epoxy cross-link adhesive may be used to bond the metal face sheet to the top of the heater. The secured metal face sheet may then be cut/trimmed to the correct size and an appropriate surface treatment (e.g., paint, primer, anodizing, etc.) may be applied.
The present invention provides an aircraft heated floor panel wherein the metal face sheet may be secured to the underlying composite structure during a high temperature curing step. In the past, this was not possible due to the differences in the thermal expansion rates between the support/heater layers and the metal layer. Specifically, at the high temperatures necessary to cure the support/heater layers, the metal face sheet would expand outwardly at a greater rate than the support/heater layers. If a high temperature film adhesive was used to secure the metal face sheet to the underlying support/heater layers, such an adhesive would lock the metal face sheet in this expanded condition. As the panel was subsequently cooled to room temperature, the bonded metal face sheet would attempt to contract inwardly thereby causing gross warping of the sheet.
More particularly, the present invention provides an aircraft floor panel comprising a plurality of layers cured together to form a lower support level and an upper heater level, a metal face sheet for protecting the top of the panel from floor-traffic related damage, and a pressure sensitive adhesive bonding the metal face sheet to the underlying support/heater layers. The support/heater layers together have a certain rate of thermal expansion and the face sheet has a different rate of thermal expansion. The pressure sensitive adhesive (or other adhesive which retains elasticity after bonding allows the different rates of thermal expansion to be accommodated during the curing and cooling steps of the manufacturing process.
In a method of making an aircraft heated floor panel according to the present invention, a layer of the adhesive is applied to the top of the heater level and the face sheet is placed thereon. The support/heater layers and the metal face sheet are then cured at an elevated curing temperature to form a composite structure whereby the face sheet expands at a different rate than the support/heater layers. When the composite structure is subsequently cooled to room temperature, the retained elasticity of the adhesive layer allows the face sheet to contract without warping or causing other damage thereto. To further streamline manufacturing procedures, the face sheet may be cut to a net shape prior and/or a surface treatment (e.g., primer, paint, etc.) may be applied prior to the curing step.
Thus, according to the present invention, a metal face sheet may be cured during the same step as the layers forming the lower support level and the upper heater level. The present invention eliminates the need for a separate bonding step for the metal face sheet and/or the need to perform this step at room temperature.
These and other features of the invention are fully described and particularly pointed out in the claims. The following descriptive annexed drawings set forth in detail certain illustrative embodiments of the invention, these embodiments being indicative of but a few of the various ways in which the principles of the invention may be employed.